This invention relates to accumulators for high pressure (say 3000 psi or higher) hydraulic systems such as used in oil well blowout preventer control systems. More particularly, the invention relates to accumulators of the type containing a guided hollow float movable in the accumulator vessel to close a shutoff valve at the bottom of the vessel to prevent the escape of precharged gas (usually nitrogen) from the vessel into the hydraulic system proper when the liquid level within the vessel becomes low.
Hollow floats used in accumulators must be vented directly to the ullage space in the accumulator vessel in order to prevent crushing when high fluid pressures are applied inside the vessel. Care must be taken to maintain the vessel in approximately an upright position to assure that the float continues to be vented directly to the ullage space and the vent outlet does not become submerged in the fill to cause flooding of the float. In the field, there is always a risk that the vessel will be inadvertently moved about or placed in a sidewise position during transport, storage or repair, causing submersion of the vent outlet and flooding of the float and, consequently, improper operation of the shut-off valve in subsequent operation of the accumulator after it is reinstated in service.
The present invention overcomes this problem by providing both a vent outlet for the float and a ballast weight for the float with the vent outlet and ballast weight on opposite sides of the center of the normally vertically extending guide means for the float, the float being mounted for free turning around such center. The result is that whatever the degree of liquid fill of the vessel, tilting of the vessel will be accompanied by turning or twisting of the float around the center of the guide means in such a manner as to keep the vent outlet above the level of the fill so that the float continues to be vented directly to the ullage space. Under normal operation of the accumulator with the vessel upright, the ballast weight is inoperative in respect of orientation of the float in any particular rotative position but, upon tilting of the vessel, the ballast weight comes into play to cause the float to turn or twist around the center of the guide means in the manner described.